U.S. Pat. Nos. 3,482,944 and 3,681,027 disclose dosimeters worn on the apparel of persons. These dosimeters have a visual read-out of the coloration of a replaceable diffusion strip. The diffusion strip is disposed in a flat box-like housing and has a chemical sensor layer. The color changes are visually evaluated in a stepwise manner by means of a comparison with color standard zones.
U.S. Pat. No. 3,920,402 discloses a sensing element of a photocolorimetric gas analyzer with the sensing element being configured so as to be impermeable to gas. This sensing element is located in a housing and the gas mixture to be analyzed is directed in intervals over the surface which is renewed each time. The radiation reflected from the surface of the sensing element is taken up by a radiation receiver and is utilized to determine the desired measuring value.
A monitoring apparatus is disclosed in German published patent application DE-OS No. 2,615,375 wherein the replaceable diffusion element is configured as a tape and, if desired, the monitoring apparatus can be provided with a built-in optical evaluation instrument. In addition, alarm systems can be connected which can be visually noticed or emit sound in order to indicate when a critical level of toxic gas in the atmosphere has been reached or is being approached.